From d3c38d90f7e7db8fbe5ec5ffbeaa97d38e177803 Mon Sep 17 00:00:00 2001
From: Allanis <allanis@saracraft.net>
Date: Sat, 12 Apr 2014 20:32:54 +0100
Subject: [PATCH] [Add] Economy now dynamically flutuates slightly.

---
 src/economy.c | 47 ++++++++++++++++++++++++++++++++++-------------
 src/space.c   |  3 +++
 src/space.h   |  3 ++-
 3 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/src/economy.c b/src/economy.c
index d4118ed..9c5f2b7 100644
--- a/src/economy.c
+++ b/src/economy.c
@@ -22,6 +22,7 @@
 #include "pilot.h"
 #include "rng.h"
 #include "space.h"
+#include "ltime.h"
 #include "economy.h"
 
 #define XML_COMMODITY_ID  "Commodities" /* XML section identifier. */
@@ -33,6 +34,7 @@
 #define ECON_SELF_RES       3.      /**< Additional resistance for the self node. */
 #define ECON_FACTION_MOD    0.1     /**< Modifier on Base for faction standings. */
 #define ECON_PROD_MODIFIER  500000. /**< Production modifier, divide production by this amount. */
+#define ECON_PROD_VAR       0.01    /**< Define the variability of production. */
 
 /* Commodity stack. */
 static Commodity* commodity_stack = NULL;
@@ -277,18 +279,39 @@ static double econ_calcSysI(unsigned int dt, StarSystem* sys, int price) {
   (void)price;
   int i;
   double I;
-  double p;
+  double prodfactor, p, pp;
+  double ddt;
   Planet* planet;
 
+  ddt = (double)(dt / LTIME_UNIT_LENGTH);
+
   /* Calculate production level. */
   p = 0.;
   for(i = 0; i < sys->nplanets; i++) {
     planet = sys->planets[i];
-    if(planet_hasService(planet, PLANET_SERVICE_BASIC))
-      p += planet->prodfactor * sqrt(planet->population);
+    if(planet_hasService(planet, PLANET_SERVICE_BASIC)) {
+      /* Calculate production.
+       *
+       * We base off the current production.
+       */
+      prodfactor = planet->cur_prodfactor;
+      /* Add a variability factor based on the gaussian distribution. */
+      prodfactor += ECON_PROD_VAR *
+        NormalInverse(RNGF()*0.90 + 0.05)*ddt;
+      /* Add a tendency to return to the planets base production. */
+      prodfactor -= ECON_PROD_VAR *
+        (planet->cur_prodfactor - prodfactor)*ddt;
+      /* Save for next iteration. */
+      planet->cur_prodfactor = prodfactor;
+      /* We base off the sqrt of the population otherwise it changes too fast. */
+      p += prodfactor * sqrt(planet->population);
+
+      /* Add it to the current system production. */
+      p += pp;
+    }
   }
 
-  /* Intensity is the production minus the consumption. */
+  /* The intensity is basically the modified production. */
   I = p / ECON_PROD_MODIFIER;
 
   return I;
@@ -322,7 +345,7 @@ static int econ_createGMatrix(void) {
       R = 1./R; /* Must be inverted. */
       Rsum += R;
 
-      /* Matrix is symetrical. */
+      /* Matrix is symetrical and non-diagonal is negative. */
       ret = cs_entry(M, i, sys->jumps[j], -R);
       if(ret != 1)
         WARN("Unable to enter CSparse Matrix Cell.");
@@ -332,7 +355,8 @@ static int econ_createGMatrix(void) {
     }
 
     /* Set the diagonal. */
-    cs_entry(M, i, i, Rsum + 1./ECON_SELF_RES);
+    Rsum += 1./ECON_SELF_RES; /* We add a resistence for dampening. */
+    cs_entry(M, i, i, Rsum);
   }
 
   /* Compress M matrix and put into G. */
@@ -350,6 +374,7 @@ static int econ_createGMatrix(void) {
 
 /**
  * @brief Initializes the economy.
+ *    @return 0 on success.
  */
 int economy_init(void) {
   int i;
@@ -361,16 +386,12 @@ int economy_init(void) {
     systems_stack[i].prices = calloc(econ_nprices, sizeof(double));
   }
 
-  /* Create the resistance matrix. */
-  if(econ_createGMatrix())
-    return -1;
-
-  /* Initialize the prices. */
-  economy_update(0);
-
   /* Mark economy as initialized. */
   econ_initialized = 1;
 
+  /* Refresh economy. */
+  economy_refresh();
+
   return 0;
 }
 
diff --git a/src/space.c b/src/space.c
index f2bee9b..0979aab 100644
--- a/src/space.c
+++ b/src/space.c
@@ -762,6 +762,9 @@ static int planet_parse(Planet* planet, const xmlNodePtr parent) {
     }
   } while(xml_nextNode(node));
 
+  /* Some postprocessing. */
+  planet->cur_prodfactor = planet->prodfactor;
+
   /* Verification. */
 #define MELEMENT(o,s) if(o) WARN("Planet '%s' missing '"s"' element", planet->name)
   MELEMENT(planet->gfx_space==NULL,             "GFX space");
diff --git a/src/space.h b/src/space.h
index 00a66d9..77d41e8 100644
--- a/src/space.h
+++ b/src/space.h
@@ -66,7 +66,8 @@ typedef struct Planet_ {
   int faction;              /**< Planet faction. */
 
   int population;           /**< Population of the planet. */
-  double prodfactor;        /**< Production factor of the planet. */
+  double prodfactor;        /**< Default production factor of the planet. */
+  double cur_prodfactor;    /**< Current real production factor of the planet. */
 
   /* Landing details. */
   char* description;        /**< Planet description. */